This invention relates generally to a highly filled fluoropolymeric jacketing compound for use as wire insulation. More particularly, this invention relates to a ceramic filled fluoropolymeric wire insulative material having uniform material properties over a wide temperature range for use in coaxial cable. This invention also relates to the coaxial cable made from this ceramic filled fluoropolymeric insulative material.
Coaxial cable is used in a variety of sophisticated and demanding electronic applications. As is well known, coaxial cable comprises an inner metal conductor surrounded by a layer of cable insulation, all of which is jacketed by a metal ground layer. In addition, an outer insulative protective covering may be applied to the ground jacketing. Presently, the cable insulation is comprised of any of a number of polymeric materials including fluoropolymeric materials such PTFE. Unfortunately, such prior art insulative compounds suffer from several important drawbacks and deficiencies. One of the more serious problems associated with prior art coaxial cable insulation is the lack of uniformity of material properties with changes in temperature. Typically, the dielectric constant varies greatly over the temperature range in which the cable is required to operate. Also, the coefficient of thermal expansion of these prior art cables is relatively high. This results in an undesirable tendency to creep under mechanical or thermal stresses as well as to undesirable fluctuation in the dielectric constant of the insulation leading to changes in the electrical operation of the cable. An example of a coaxial cable insulative material exhibiting such undesirable properties is a solid PTFE insulation.